A Revision of the Genus Trollius (Ranunculaceae) in Japan

Abstract

The genus Trollius (Ranunculaceae) in Japan is taxonomically revised. Plants belonging to the genus predominantly grow in grasslands of montane and alpine zones (higher than 1500 m) in Japan. However, in the lowlands of Hokkaido, northern Japan, Trollius plants were also found along rivers. Among such fluvial plants two species are newly recognized; T. soyaensis Kadota in the Dohoku area and T. teshioensis Kadota extending from the Dohoku to the Doto areas. A new section, sect. Yezoinsulicola Kadota, is proposed based on the two species; T. soyaensis and T. teshioensis. Plants from Rebun Island, northern Hokkaido, have been frequently attributed to the Asian continental species, T. ledebourii Rchb. or T. ledebourii Rchb. var. polysepalus Regel & Tiling, mainly due to the petals being longer than the stamens. However, the petals are somewhat fleshy and are equipped with well-developed nectary pits. The sepals are many in number (7–13) and ascending incurvedly, hence the flowers are bowl-shaped. On the contrary T. ledebourii has patent sepals and the flowers are flat and saucer-shaped. Thus the plants from Rebun Island represent an undescribed species belonging to sect. Insulaetrollius Drosz. distributed in Far East Asia. This new species is described as T. rebunensis Kadota. The plant called ‘Shinano-kinbai’ in Japanese is a representative of Japanese alpine plants. The name Trollius japonicus Miq. has been adopted for this plant. It happens that the type specimen derived from ‘Jeso’ (= Hokkaido, Japan) has follicles with short and straight beaks and developed keels. Thus the type specimen of T. japonicus should be ascribed to T. riederianus Fisch. & C. A. Mey. Consequently a new name, T. shinanensis Kadota, is proposed for ‘Shinano-kinbai’ based on the collection from Mt. Asahi-dake, Itoigawa-shi, Niigata Pref., central Honshu, Japan. In total four sections and eight species are recognized in the genus Trollius in Japan.